Showing papers by "Nicholas Asher published in 2017"

How much progress have we made on RST discourse parsing? A replication study of recent results on the RST-DT.

Abstract: This article evaluates purported progress over the past years in RST discourse parsing. Several studies report a relative error reduction of 24 to 51% on all metrics that authors attribute to the introduction of distributed representations of discourse units. We replicate the standard evaluation of 9 parsers, 5 of which use distributed representations, from 8 studies published between 2013 and 2017, using their predictions on the test set of the RST-DT. Our main finding is that most recently reported increases in RST discourse parser performance are an artefact of differences in implementations of the evaluation procedure. We evaluate all these parsers with the standard Parseval procedure to provide a more accurate picture of the actual RST discourse parsers performance in standard evaluation settings. Under this more stringent procedure, the gains attributable to distributed representations represent at most a 16% relative error reduction on fully-labelled structures.

Message Exchange Games in Strategic Contexts

Abstract: When two people engage in a conversation, knowingly or unknowingly, they are playing a game. Players of such games have diverse objectives, or winning conditions: an applicant trying to convince her potential employer of her eligibility over that of a competitor, a prosecutor trying to convict a defendant, a politician trying to convince an electorate in a political debate, and so on. We argue that infinitary games offer a natural model for many structural characteristics of such conversations. We call such games message exchange games, and we compare them to existing game theoretic frameworks used in linguistics—for example, signaling games—and show that message exchange games are needed to handle non-cooperative conversation. In this paper, we concentrate on conversational games where players’ interests are opposed. We provide a taxonomy of conversations based on their winning conditions, and we investigate some essential features of winning conditions like consistency and what we call rhetorical cooperativity. We show that these features make our games decomposition sensitive, a property we define formally in the paper. We show that this property has far-reaching implications for the existence of winning strategies and their complexity. There is a class of winning conditions (decomposition invariant winning conditions) for which message exchange games are equivalent to Banach- Mazur games, which have been extensively studied and enjoy nice topological results. But decomposition sensitive goals are much more the norm and much more interesting linguistically and philosophically.

ANNODIS and related projects: case studies on the annotation of discourse structure

Abstract: In this paper we report on the efforts of three projects to annotate texts and dialogues with discourse structure. We provide a theoretical discussion of various alternatives and then present our approach to discourse structure annotation, along with some applications of the resources that we have developed.

Types, Meanings and Co-composition in Lexical Semantics

Abstract: This paper investigates co-composition, the composition of a predicate and its arguments in which either the predicate, the arguments, or both shift their meaning. We study the implications of this phenomenon for type-theoretic approaches to semantics. We adduce evidence from distributional methods in lexical semantics that co-composition is widespread and then argue that a proper treatment leads to a reconsideration of the basics of type theory for natural language semantics.

Conversation and Games

Abstract: In this paper we summarize concepts from earlier work and demonstrate how infinite sequential games can be used to model strategic conversations. Such a model allows one to reason about the structure and complexity of various kinds of winning goals that conversationalists might have. We show how to use tools from topology, set-theory and logic to express such goals. We then show how to tie down the notion of a winning condition to specific discourse moves using techniques from Mean Payoff games and discounting. We argue, however, that this still requires another addition from epistemic game theory to define appropriate solution and rationality underlying a conversation.